Data transmitting apparatus and data transmitting method

ABSTRACT

A parity bit generating section  110  generates parity bits of FEC for error correction from transmission data. A transmission power deciding section  111  decides transmission power at the time of retransmitting the parity bits from the number of information bits of transmission data and the number of parity bits. A transmission power controller  112  controls transmission power based on information decided by the transmission power deciding section  111  and outputs the resultant to a radio transmission section  104.

TECHNICAL FIELD

The present invention relates to a data transmitting apparatus and adata transmitting method suitable for use in a communication terminalapparatus and a base station apparatus of a mobile communication system.

BACKGROUND ART

As an error correcting method in data transmission, for example, thereis a method called a type II hybrid ARQ method (Shuichi Sasaoka: MobileCommunications, page 240, Ohmsha,Ltd). In this error correcting method,only information bits are first transmitted, and then when it isnecessary to perform retransmission with respect to the transmission(namely, when a receiving side cannot demodulate the information bitscorrectly), only parity bits (redundant bits) of FEC (Forward ErrorCorrection) for error correction are retransmitted. The receiving sideperforms error correction using information bits previously received andthe parity bits that have just received.

In the conventional data transmitting method, however, the transmissionof information bits and the retransmission of parity bits are performedwith the same power, causing a problem in which interference, which isequivalent to or more than interference caused at the time oftransmitting information bits, will be given to other users at the timeof retransmitting the parity bits. In particular, since the number ofparity bits is generally smaller than that of information bits,transmission power per parity bit becomes higher than transmission powerper information bit when transmission of information bits and that ofparity bits are performed with the same power. This results in that theparity bits are retransmitted with transmission power more thannecessary, thereby causing the aforementioned problem.

As a more specific explanation, for example, if information bits aretransmitted with power P where the number of information bits is 1000and that of parity bits is 10, power per bit becomes P/1000. Also, ifthe retransmission of parity bits is performed with the same power P,power per bit becomes P/10, resulting in an increase of transmissionpower as compared with information bits. In this way, in a case wheretransmission is performed with the same power P, power per bit of paritybits becomes higher than that of information bits, increasing in apossibility that interference, which is equivalent to or more thaninterference caused at the time of transmitting information bits, willbe given to other users at the time of retransmitting the parity bits.Additionally, this problem occurs not only in the type II hybrid ARQmethod but also in all methods in which the same power is used at thetransmission data transmitting and retransmitting time.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a data transmittingapparatus and a data transmitting method that are capable of restraininginterference with other users to a minimum at the time of retransmittingtransmission data.

This object can be achieved by controlling transmission power at thetime of retransmitting data after transmitting the data.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing each of a base station apparatus and acommunication terminal apparatus according to Embodiment 1 of thepresent invention;

FIG. 2 is a view explaining data transmission in the base stationapparatus according to Embodiment 1 of the present invention; and

FIG. 3 is a block diagram showing each of a base station apparatus and acommunication terminal apparatus according to Embodiment 2 of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The following will specifically explain the best mode for carrying outthe invention with reference to the drawings accompanying herewith.

(Embodiment 1)

FIG. 1 is a block diagram showing each of a base station apparatus and acommunication terminal apparatus according to Embodiment 1 of thepresent invention.

In FIG. 1, a base station apparatus 100A comprises a buffer 101 fortemporarily storing transmission data, a transmission frame generatingsection 102 for generating a transmission frame, a modulating section103 for modulating the transmission frame generated by the transmissionframe generating section 102 so as to generate a modulated signal, aradio transmission section 104 for amplifying the modulated signalgenerated by the modulating section 103 up to power with a predeterminedlevel so as to output the resultant, a duplexer 105 for assigning anantenna 106 to a transmission system or reception system, antenna 106, aradio reception section 107 for receiving a radio signal captured by theantenna 106 so as to output a modulated signal, a demodulating section108 for demodulating the demodulated signal received by the radioreception section 107, a separating section 109 for separating receptiondata, and a transmission request signal that is called an ACK(Acknowledgement) signal or a retransmission request signal that iscalled a NACK (Negative Acknowledgment) signal from the signaldemodulated by the demodulating section 108, a parity bit generatingsection 110 for generating parity bits (redundant bits) of an errorcorrecting code (FEC: Forward Error Correction) for error correctionfrom transmission data, a transmission power deciding section 111 fordeciding transmission power at a parity bit retransmitting time from thenumber of information bits of transmission data and that of parity bits,and a transmission power controller 112 for controlling the radiotransmission section 104 so as to obtain transmission power decided bythe transmission power deciding section 111.

Additionally, the radio transmission section 104 corresponds totransmitting means. Moreover, the transmission power deciding section111 and transmission power controller 112 configure transmission powercontrolling means.

On the other hand, a communication terminal apparatus 100B comprises anantenna 113, a duplexer 114 for assigning the antenna 113 to atransmission system or a reception system, a radio reception section 115for receiving a radio signal captured by the antenna 113 so as to outputa modulated signal, a demodulating section 116 for demodulating datafrom the modulated signal output from the radio reception section 115, adata storing section 117 for storing data demodulated by thedemodulating section 116, an error detecting section 118 for detectingdata stored by the data storing section 117 and an error of data errorcorrected by an error correcting section 122, transmission framegenerating section 119 for generating a transmission frame fromtransmission data, and an ACK signal or NACK signal, a modulatingsection 120 for modulating the transmission frame generated by thetransmission frame generating section 119 so as to generate a modulatedsignal, a radio transmission section 121 for amplifying the modulatedsignal from the modulating section 120 up to power with a predeterminedlevel so as to output the resultant, and the error correcting section122 for correcting an error of data stored by the data storing section117.

In the base station apparatus 100A, after input transmission data isstored in buffer 101, the transmission data is not subjected to errorcorrecting coding, and a transmission frame is generated only using thetransmission data in transmission frame generating section 102.

The generated transmission frame is modulated by the modulating section103, the resultant is amplified up to power with a predetermined levelby the radio transmission section 104, and the radio signal istransmitted from the antenna 106 via the duplexer 105.

In the communication terminal apparatus 100B, a radio signal captured bythe antenna 113 is received by the radio reception section 115 via theduplexer 114 so as to output a modulated signal. The modulated signaloutput from the radio reception section 115 is demodulated by thedemodulating section 116 and the resultant is stored in the data storingsection 117. Data stored in the data storing section 117 is subjected toerror detection by the error detecting section 118. In a case wherethere is an error in the data stored in the data storing section 117, aNACK signal is input to the transmission frame generating section 119from the error detecting section 118. The transmission frame generatingsection 119 generates a transmission frame from the input NACK signaland transmission data. The transmission frame generated by thetransmission frame generating section 119 is modulated by the modulatingsection 120, the resultant is amplified up to power with a predeterminedlevel by the radio transmission section 121, and the radio signal istransmitted from the antenna 113 via the duplexer 114.

In the base station apparatus 100A, a radio signal captured by theantenna 106 is received by the radio reception section 107 via theduplexer 105, and a modulated signal is output from the section 107. Themodulated signal output from the radio reception section 107 isdemodulated by the demodulating section 108. Demodulated data is inputto the separating section 109 to be separated into received data andNACK signal, and received data is output directly and NACK signal isinput to the buffer 101. When the NACK signal is input to the buffer101, the transmission data stored in the buffer 101 is input to theparity bit generating section 110. Then, a parity bit of errorcorrecting code for error correction is generated from the transmissiondata by the parity bit generating section 110, and the resultant isinput to the transmission frame generating section 102.

Moreover, the number of information bits for the transmission data andthat of parity bits are input to the transmission power deciding section111 so as to decide transmission power at the parity bit retransmittingtime from these numbers of bits. For example, it is assumed that thenumber of information bits for transmission data is set to “1000”, thenumber of parity bits is set to “10”, and transmission data is sent withpower P. Power per information bit results in P/1000. In retranslatingthe parity bit, the power is decided to P/100 so that power per bit isthe same in the parity bit and transmission data. Thus, a ratio of thepower of transmission data to the power of parity bit is made the sameas a ratio of the number of information bits to the number of paritybits (namely, transmission power per bit is made the same as eachother).

Transmission power information decided by the transmission powerdeciding section 111 is input to the transmission power controller 112.The transmission power controller 112 controls transmission power of theradio transmission section 104 based on input transmission powerinformation. While, the parity bits generated by the parity bitgenerating section 110 are input to the transmission frame generatingsection 102 so as to generate a transmission frame. The generatedtransmission frame is modulated by the modulating section 103 and theresultant is input to the radio transmission section 104. The modulatedsignal input to the radio transmission section 104 is transmitted withtransmission power controlled by the transmission power controller 112from the antenna 106 via the duplexer 105.

In the communication terminal apparatus 100B, when the parity bitsretransmitted from the base station apparatus 100A are received, datastored in the data storing section 117 and the parity bits are input tothe error correcting section 122 and error correction is providedthereto. Data subjected to error correction is input to the errordetecting section 118 and error detection is provided thereto. A seriesof operations is repeated until no error is detected by the errordetecting section 118, and when no error is detected, data subjected toerror correction is output as received data, while the content of datastoring section 117 is reset. Then, an ACK signal for requesting nextdata transmission is input to the transmission frame generating section119 from the error detecting section 118 so as to generate atransmission frame together with data transmission.

In the base station apparatus 100A, when the ACK signal is received, itis input to the buffer 101 and the content of the buffer is reset.Resultantly, transmission of next data is started.

FIG. 2 illustrates a difference in power between information bits andparity bits.

When a NACK signal is received after transmitting information bits,transmission power for parity bits is decided and the parity bits aretransmitted with the decided power. Additionally, in this case, it isassumed that the number of parity bits is smaller than that ofinformation bits. When an ACK signal is received after transmitting theparity bits, next information bits are transmitted with the same poweras that of the previous information bits (or power decided bytransmission power control).

Thus, according to this embodiment, in a case where a need forretransmitting transmission data arises and only parity bits of errorcorrecting code for error correction are transmitted, transmission powerof parity bits is set to be lower than that of data transmission, sothat interference with other users caused by transmission of parity bitscan be restrained to a low level.

Additionally, in this embodiment, the base station apparatus 100A andcommunication terminal apparatus 100B may be reversed each other. Inother words, 100A and 100B may be used as the communication terminalapparatus and base station apparatus, respectively.

(Embodiment 2)

FIG. 3 is a block diagram showing each of a base station apparatus and acommunication terminal apparatus according to Embodiment 2 of thepresent invention. In this figure, parts identical to those in FIG. 1are assigned the same codes as in FIG. 1 and their detailed explanationsare omitted.

Though the aforementioned Embodiment 1 decides the power ratio betweentransmission data and parity bits, as a transmission power decidingmethod at the time of retransmitting the parity bits of FEC, based onthe ratio between the number of information bits of transmission dataand that of parity bits, Embodiment 2 decides it based on receptionquality information in addition to the ratio between the number ofinformation bits of transmission data and that of parity bits.

In a communication terminal apparatus 100C, a modulated signal receivedby the radio reception section 115 is demodulated by the demodulatingsection 116 and reception quality is measured by a reception qualitymeasuring section (reception quality measuring means) 301. Datademodulated by the demodulating section 116 is stored in the datastoring section 117. Meanwhile, reception quality information measuredby the reception quality measuring section 301 is input to thetransmission frame generating section 119, and a transmission frame isgenerated together with an ACK signal or NACK signal and transmissiondata.

On the other hand, in the base station apparatus 100A, a modulatedsignal received by the radio reception section 107 is demodulated by thedemodulating section 108. Data demodulated by the demodulating section108 is separated into received data, and an ACK signal or NACK signaland reception quality information. The received data separated is outputdirectly, and ACK signal or NACK signal is input to the buffer 101, andreception quality information is input to the transmission powerdeciding section 111.

The transmission power deciding section 111 decides transmission powerusing the reception quality information. For example, even iftransmission power is decided in the same way as that of theaforementioned Embodiment 1, power higher than decided transmissionpower is set when reception quality is poor from reception qualityinformation, and power smaller than decided transmission power is setwhen reception quality is good. It is thereby possible to decrease aprobability that errors will occur in parity bits when reception qualityis poor, and to reduce interference with other users by lowering powerwhen reception quality is good.

Additionally, in this embodiment, the base station apparatus 100A andcommunication terminal apparatus 100C may be reversed each other. Inother words, 100A and 100C may be used as the communication terminalapparatus and base station apparatus, respectively.

Moreover, in the aforementioned Embodiments 1 and 2, the transmissionpower is controlled so that the transmission power per bit is the samein transmitting transmission data and parity bits. However, it is notnecessary to make the transmission power per bit the same always. Forexample, transmission power of parity bits may be increased or decreasedas compared with the ratio between the number of information bits oftransmission data and that of parity bits. In this case, if transmissionpower of parity bits per bit is high, error correction ability increasesbut interference with other users becomes greater. Conversely, iftransmission power of parity bits per bit is low, interference withother users becomes smaller but error correction ability decreases.

Further, transmission power may be increased with respect to data whosedelay in retransmission is not permitted, and decreased with respect todata whose delay in retransmission is permitted. Transmission power maybe appropriately changed with consideration given to these points.

Furthermore, in the aforementioned Embodiments 1 and 2 both ACK and NACKsignals are sent back. However, it is not necessary to send back theNACK signal always. For example, when such a system is used that data isretransmitted unless ACK signal comes within a predetermined time aftertransmitting data, it is not unnecessary to send back the NACK signal.

Still furthermore, in the aforementioned Embodiments 1 and 2, the firsttransmission is limited to information bits subjected to no errorcorrection and retransmission is limited to the parity bits. However, itmay be possible to transmit information bits and parity bits in thefirst transmission and/or in the retransmission.

As explained above, according to the present invention, interferencewith other users can be restrained to a minimum at the time ofretransmitting transmission data to make it possible to implement goodcommunications.

This application is based on the Japanese Patent Application No.2000-190229 filed on Jun. 23, 2000, entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a communication terminalapparatus and a base station apparatus of a mobile communication system.

1. A data transmitting apparatus comprising: a transmitting section thatamplifies a modulated signal, obtained by modulating transmission data,up to power with a predetermined level so as to transmit the amplifiedsignal; and a transmission power controlling section that controlstransmission power at a time of re-transmitting said transmission data,wherein: said transmission power controlling section decides thetransmission power of parity bits based on a ratio of the number ofinformation bits to the number of parity bits when said parity bits forerror correction are transmitted at the transmission datare-transmitting time.
 2. The data transmitting apparatus of claim 1,wherein said transmission power controlling section uses receptionquality information, sent from an apparatus receiving the transmittedtransmission data, in connection with the modulated signal transmittedfrom the data transmitting apparatus at the time of deciding thetransmission power of parity bits.
 3. The data transmitting apparatus ofclaim 2, wherein: said transmission power controlling section decidesthe transmission power of parity bits according to the reception qualityinformation, increases said transmission power when the receptionquality is poor, and decreases said transmission power when thereception quality is good.
 4. A data transmitting apparatus comprising:a transmitting section that amplifies a modulated signal, obtained bymodulating transmission data, up to power with a predetermined level soas to transmit the amplified signal; and a transmission powercontrolling section that controls transmission power at a time ofre-transmitting said transmission data, wherein: said transmission powercontrolling section decides the transmission power of parity bits suchthat a ratio of the transmission power of information bits to the powerof parity bits and a ratio of the number of information bits to thenumber of parity bits become the same value when said parity bits forerror correction are transmitted at the transmission datare-transmitting time.
 5. The data transmitting apparatus of claim 4,wherein said transmission power controlling section uses receptionquality information, sent from an apparatus receiving the transmittedtransmission data, in connection with the modulated signal transmittedfrom the data transmitting apparatus at the time of deciding thetransmission power of parity bits.
 6. The data transmitting apparatus ofclaim 5, wherein: said transmission power controlling section decidesthe transmission power of parity bits according to the reception qualityinformation, increases said transmission power when the receptionquality is poor, and decreases said transmission power when thereception quality is good.
 7. A base station apparatus comprising thedata transmitting apparatus of claim 1.